Aircraft engine and propeller control system



J. STUART UI Jan. 5, 1954 AIRCRAFT ENGINE AND PROPELLER CONTROL SYSTEM 6 Sheets-Sheet l Filed DeC. 5, 1945 ne I |||||||||||||||||il ERE 752 5% NS J. STUART DI Jan. 5, 1954 AIRCRAFT ENGINE AND PROPELLER CONTROL SYSTEM Filed DBG. 3, 1945 6 Sheets-Sheet 2 Jan. 5, 1954 STUART ]1[ 2,664,959

AIRCRRFT ENGINE AND PROPELLER CONTROL SYSTEM Filed Dec. 3, 1945 6 Sheets-Sheet 3 n INVE TOR 4/ ATTORNEY/4 Jan 5, 1954 J. STUART 111 AIRCRAFT ENGINE AND PROPELLER CONTROL SYSTEM 6 Sheets-Sheet 4 Filed Dec. 3, 1945 NWN,

1N ENToR. W' 7/ ATToRNEY/ MSN.

Jan. 5, 1954 I J, STUART m 2,664,959

AIRCRAFT ENGINE AND PROPELLER CONTROL SYSTEM Filed Deo. 3, 1945 6 Sheets-Sheet 5 ff j? fff #fil/V w 97 0 .v

@ zdf/3 lNvE TOR m w*iff* a BY gt /416 ATToR-NEY/ Jan. 5, 1954 J. STUART 111 2,664,959

AIRCRAFT ENGINE AND PROPELLER CONTROL. SYSTEM Filed Dec. 3, 1945 6 Sheets-Sheet 6 IN ENTOR M Z2 ATTORNEY( Patented Jan. 5, 1954 AIRCRAFT ENGINE AND PROPELLER CONTROL SYSTEM Joseph Stuart III, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Mich., a cor-- poration of Delaware Application December 3, 1945, Serial No. 632,566 A 23 Claims. (Cl. V70-135.74)

This invention relates to the control of the speed of a prime-mover propeller power plant particularly for use in airplanes.

An object of the present invention is to provide a system of speed control having stability of operation which provides for quick correction of speed error even with internal combustion turbines or other prime-movers having relatively high inertia. This object is accomplished by an hydraulic blade angle controller and by an hydraulic fuel-controller using the same pressure fluid, the flow rate to each controller being under the control of a speed-sensitive valve whereby the rate of change of blade angle and the change of fuel setting (engine torque) is proportional to the amount offspeed. Since the two servos operate on the same pressure fluid whose now-rate is being controlled by the same speed responsive valve, the control system is free from discrepancies and errors.

Another object is to provide for governed speed both in the positive thrust range and in the negative thrust range, and more particularly to provide for operation of a turbine at substantially full or best operating speed throughout the ranges from zero thrust to full positive thrust and to full negative thrust.

Another obj ect is to prevent shift from the positive range of control to the negative range of control at excessive forward speeds when the propeller would windmill the prime-mover excessively.

Another object is to provide manual control of propeller blade angles in the low blade angle range where governed control is not satisfactory.

Another object is to provide control apparatus having a single manually operated main control member for the negative thrust range, for the positive thrust range and for feathering.

Another object is to provide a control system which permits manual selection of appropriate low or negative blade angles requiring low consumption of power by the propeller in order to facilitate starting the prime-mover. This is particularly desirable when starting a turbine.

Another object is to provide means for modifying the speed setting of the manually operated main control member in order to reduce speed when desirable for sake of economy.

A further object is to provide a control system adapted either for single-engine control or for multi-engine control. In this connection, a further object is to provide for the synchronization of several engines, each having the controls embodying the invention Whose objects hereinbefore have been stated, while providing for control of the engines individually independently of the synchronizing apparatus. l The system provides certain safety features which prevent abnormal operation of any of the engines in the event of failure of the synchronizing apparatus. A further object is to provide for synchronization in the negative thrust range as well as in the positive thrust range.

A further object is to provide for pitch indications in the cockpit.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein a preferred embodiment of the present invention is clearly shown.

In the drawings:

Fig. l is a diagram of the present control system.

Figs. 2 and 3 are longitudinal sectional views in different planes of the servo-motor |40 of Fig. l.

Figs. 4 and 5 are diagrams of optional gear trains to be used with apparatus shown in Fig. l.

Fig. 6 is a diagram of apparatus for plural engine control.

Fig. '7 is a sectional view on line 'I-T of Fig. 6.

Figs. 8 through 11 are charts showing the operation of the control system under various conditions.

Fig. 12 is a perspective, longitudinal, sectional view of a form of propeller hub and torque unit assembly with which the present control apparatus may be used.

Fig. 13 is a fragmentary sectional view taken approximately on line III-I3 of Fig. l2.

Figs. 14, 15, and 16 are fragmentary sectional views taken respectively on lines Ill-I4, I5-I5, and IE--IG of Fig. 13.

Fig. 17 is a fragmentary view in the direction of arrow II of Fig. 16.

Fig. 18 is a fragmentary longitudinal sectional view showing a modified form of piston of Fig. 1 equipped with automatic oriiice control.

Fig. 19 is a view in the direction of arrow I9 of Fig. 18.

Fig. 20 isa sectional view on line 20-20 of Fig. 18.

0f Fig. 18.

Referring to Fig. 1, a shaft I Il driven by the I engine shaft drives an oil pump II, a gear I2 and a bevel gear I3 meshing with bevel gears I4 and I5 supported by a gear I 1 and meshing with a gear I8 driven by a three-phase syn-,

3 chronous motor I9 operated by a master generator (to be described) which is driven by an elec-- tric motor at a predetermined speed for the purpose of synchronizing or equalizing the governed speeds of the engines of the multi-engine airplanes. So long as the speed of gears I3 and I8 are equal and' opposite there Willbenov rotation oi' gear H, but this gear will rotate in one di-` rection or the other, depending on the difference in the speeds of gears I8 and I3.

pinion 28 meshing with racks 29 and 30. Rack 29 is engaged by pinion 3| pivotal'ly supported: by. rod 32 and meshingy with a rack 33 actuated between stops 34 and 35 by a lever 35 pivoted 'at31.V

The gear I2 meshes with a gear 40 connected by links 4| withi iiy-'weights42t connected-'by links 43 with al collar'44 attached to a valvel stein'v 6| respectively with pipes' $5' and 66, or vice versa. Valve meinber`164-islactuated bya link G1 connected vwith 'a leverlilv pivoted at 59.

Pipes 35"aiid 'are connectedwith cylinder'H of a servo motor 'IIJ having a, piston- '|2conn`ected with rods`|3 an'd'-'|4.' RodM'is'connected with a rack 'l5 meshing with a gear 76 which operates shaft 'I'I connected vwitha Ibl'aclefpi'mih-foontrol unit to be'desc'ribed. Shaft?? operat'esfar'i instrument 18 known asa fse'lsyn" fortransmitting tothe instrument board an indication of'blade pitch Relief valves-1 19? limit theoil pressures exerted on piston 12. These' valves open at such lowpressure thatflov-rate is not appreciably curtailed' although thefpiston -12v is at the end of its travel. Bladefariglefinayy be controlled manually although pressure maybe' applied to the piston 12; This' will be"'d'scrib'ed later.

Centrifugal forcfaetin'gfori weights 42`is op-l posed by spring 42a and is assistedby'springf42h;- The compression' of the sprili`g42b is'adjusted by movements oi rod 32 transmitted through a thrust bearing 42e 4to thefspring 42h.-

A main controllever 85-pivoted7at8| nievesv along a quadrant sector 82 havin'ga'cieathering stop 83A and a transition's'tpfM' engaged by a plunger (not shown) carried' by the lever B9. By pressing a button 55', theplun'ger isretracted so that the'lever'fimay-Inoveclockwi'se past the stop intofeather'con-trollingposition orv countercl'ockwise past the'. stop 84 -into negative thrust controlling position. Stops 83 and B4 Gear meshes with gear 2|l connected by a friction-clutch 2| with a screw 22 engaged by a nut`23`,` connected` by a link 24 with a lever 25 movable between limit stops 25a and 25b and'pivotally-supp'orted'- by a link 25 pivoted at 21.' Lever ZElcarriesa' Guide 48 has port`s152 'an'd53 connectedl re- 4 tive pitch control, a portion 92 for transition between negative pitch control and positive pitch control, a portion 92- ior coordinating throttle setting with positive pitch control and a portion 54 for coordinating throttle setting with feathering control. This cani groove receives a roller 95.

Plateiprovides a cam groove having-a poi'- tion` |0| controlling speed for negative pitch, a transition groove |52, a portion |53 for controllin'g speed for positive pitch and a portion |54 controlling speed for feathering. Portions |0l, |32 andf|||3 are for turbine control. Portions |02", and |03' are for reciprocating engine control.v This' ca-in groove receives a roller |85 carried by the rack- Si).

'I'he'cainplate IIe provides a cam groove of varying-Width' bounded on the upper side by the walls ||5, IIS, II'I and IIS, and on the lower side'by wallsl I2, ||4, IIS and |25. This irregular cam groove receives a roller |2| supported by rediff'. v The-portion bounded by walls III, and ||2'fprovides 'the'blade angle limiting' portion for negative pitch control. walls |4'and ||54 isatransition gate ior receiving'roller |2| when conditions are proper for changeibetweenpositive and negative pitch'control or-'vice versa. IIS, I|'| and V| i6" provides the portion for limiting the blade angle for positive pitch control. The portion boundedfbyv/alls ||9 and |23 vlimits the blade angle for feathering.y

Tlieiplate I I3' provides a cam groove |22 receivihga'roller |23 on lever '68. When shifting intonegative pitch control, cam |22v raises roller |23-and causes lvalve E2toreverse the connections with cylinder 'I I.

rhe roller 95' which is received grooveofp-late 96 is carried by a` tached to a lever- |3| having a -Boatingiulcrum |32an`d conn'ected'by a'linl: |33 with a plate in the cam I 34 having a throttle actuating cam groove |351' for receiving -a roller |36 mounted cna rod |31' connected in any suitable manner with the throttlev mechanism of the prime-mover, either the throttle valve 'oi a carburetor reciprocating engine orthe fuel flow control valve of a fuel injection reciprocating engine or a gas turbine.

The oating fulcrum |32 of lever |3| is supported by a link |38 connected' with a lever |39 pivotedat |3911. Lever |39 is connected'with the'ipis'ton'rod' |4'I'of a servo-motor |40. Rod |4| is attachedto a piston |42 movable inthe axially fixed cylinder |43. The pressure fluid for moving the 'piston in either direction enters the side'of cylinder |43? through a pipe I44connected with pump outlet 50. Pipe |44comrnunicates with an `annular groove |45 provided by the piston |42. Groove |45 is connected by passages |46 with diametrically opposite grooves |47 provided by the piston rod |4I. Grooves |41 are connected by diametrically opposite holes |48 with the interiorof the rod |4I. Rod I4| receives a -valve |49 having lands |50 and |5| and connected by bell-crankl 52 and link |53 with the piston 5'!k within the cylinder 56. Referring to Fig. 2 which is a longitudinal sectional view 0f the servo-motor |4Il` in a plane 120 from the plane of the sectional View shown in Fig. 1, the land |5| controls diarne-trically opposite ports |54 connected with diametrically opposite grooves |55 ofthe rod |4I; and grooves |55-v are connected'byholes |56 with the upper end of the cylinder |4V3asV viewed in Fig. 2. Referring to Fig. 3, which shows -a longitudinal sectional view taken in'aiplane 120 with respect'to the planes The portion bounded by The portion bounded by wallsA rod |33 atof the longitudinal sectional views of Figs. 1 and 2, the land |50 controls ports |51 connected with diametrically opposite grooves |58 of the rod |4| and grooves |58 are connected by holes |59 with the lower end of the cylinder |43.

As the valve |49 moves, thepiston |42 follows the valve. For example, if valve |49 moves down the ports |54 are uncovered, and pressure fluid is admitted to the upper end of cylinder |43 to cause piston |42 to move down the distance rthat valve |49 had moved down. Fluid in the lower end of the cylinder escapes through holes |59, grooves |58, ports |51 and the upper end of rod |4|. If valve |49 moves up, ports |51 are nncovered, and pressure fluid is admitted to the lower end of cylinder |43 to cause piston I 42 to move up the distance that valve |49 had moved up. Fluid in the upper end of cylinder |43 escapes through holes |56, grooves |55, ports |54 and holes |60 in the rod |4|.

The pressure fluid which is Idischarged from the rod 4| is received by suitable chambers, not shown, which enclose the servo-motor |40, the pressure fluid being returned to the intake of the pressure pump l. The discharge from the valve sleeve 48 is likewise received by a reservoir enclosing the pump l.

'I'he valve |49 is actuated by the piston 51 in the cylinder 56. The piston 51 moves right when oil flows from the pipe 54 through the cylinder 5G and into the pipe 6|; and piston rod |4| and cam |34 move up and rod |31 moves right to close the fuel valve or throttle. Piston 51 moves left when this flow is reversed; and the cam |34 moves down to open the fuel throttle. If the total oil pressure acting upon the piston 51 were sufcient to operate the engine throttle through the cam plate |34, the servo-motor unit |40 could be omitted and the piston 51 would be directly connected with the lever arm |39.

An explanation of the various legends appearing on Fig. 1 will now be made. The negative, transition, positive and feathering portions of the cam grooves of plates 90, |00 and ||0 are respectively indicated by the double arrow lines marked respectively N, T, P and F. The posi' tive range of the main control lever 80 is indicated by the double arrow arc marked positive The negative range of the main control lever 80 is indicated by Ithe double arrow arc marked negative The extreme positions of the roller |36 within the throttle actuating cam groove |35 are indicated respectively by vertical dot-dash lines marked throttle closed and wide open throttle. The movement of the piston rod |4| of the servo-motor |40 to correct an over-speed is indicated by the arrow marked over-speed. The movement of rod |4| to correct for underspeed is indicated by the arrow marked underspeed. The movement of valve rod 45 to correct over-speed is up, as indicated by the arrow marked over-speed. The movement of Valve rod 45 to correct under-speed is down, as indicated by the arrow marked under-speed. Adjacent the rod 32 are two arrows marked respectively decreases and increases indicating, respectively, the movement for equilibrium speed decrease or increase. The direction of rotation of the shaft |0 is indicated by arrow |0a. The direction of rotation of gear I8 is indicated by arrow |8a. Looking down upon the gear 20 the direction of rotation to correct over-speed relative to the master is counterclockwise, as indicated by thel arrow marked overspeed; and, to correct for under-speed, the directionA oi rotation of gear 20 is clockwise, as indicated by the arrow marked underspeedr The flow of pressure oil through the pipes 55 and 6| to correct over-speed is indicated by the adjacent yarrows marked overspeed; and the direction of ow to correct under-speed is indicated by the adjacent arrows marked underspeed. The direction of movement of rack 15 to obtain increased pitch or decreased pitch are indicated by arrows respectively marked by appropriate legends.

The downward movement of rod 32 for the purpose of increasing equilibrium speed is limited by lug 32a which engages a stop 3211, to prevent any unsafe maximum speed being called for.

In order to understand the function of the control apparatus with respect to stability of Agovern.- ing action, reference is made to the fundamental equation ofthe power plant and. controller combination whichis:

J :polar moment of inertiaof all rotating parts referred to the propeller shaft axis.'

=angular displacement (radians) of the-rotating mass relative to a reference rotating at constant speed.

t or -=velooity of displacement (radians/sec.) gt or %5=acceleration of displacement (mamans/sec?) Q1=torque due to off-speed. l

Q increment of torque due to off-speed D43 increment of velocity of displacement =blade angle change Q2=torque due to blade angle change @Q2 increment of torque due to blade angle change increment of blade angle change Torque I due to acceleration=J '43 Qi f Torque II due to speed error--X QZ Torque III due to blade angle change- The algebraic sum of Torques I, II and III is zero in free motion of the system.r

The only variable is Torque I varies with acceleration of Torque -II varies with velocity of (d) Torque III varies with amount of qi, (rp) Torque II representsthe'sum of the effect of aerodynamic damping and of throttle control by piston 51 (Fig. l). Piston 51 effectsa throttle control in response to velocity of flow of pressure oil entering or leaving cylinder 1| It is responsive to .velocity of displacement; and

fthe-rate of `movement of the piston 51.

the springs.

ammo@ 7 as engine borquefisaarfunctionof throttle settingZ a correcting Itorque proportional -toI `offspeed,-fi5y results.

Torque lIII :represents -the function of piston J2 AftFig. i1) vwhich lchangesfblade -angleinprolportion to the amount of l displacement.

This meansl that' the y-Weightsfin respond- 'ing to an increaselorl decrease'in speed, actuates the -valve 4member 45 in :proportion yto :off-speed. In so moving the valve-.adirects'llow' of'ffiuidffrom the source |I in proportion '-to fol-speed,"-or in .proportion'tospeed error. "I'heflow from valve IBLis'directed-either' by E54: to -cylinder "56 and'V then by .8| :.tofcylin'der =1| vv-here it displaces piston `i12 incproportionto IspeedA error, ori-itI isfdirectedv by $5 :to :cylinder '17| :where itV also displacesx piston J 2 fin proportion to speed error. "Thus `the f rate of iud lilow 'to the :cylinder'1 I 1 is :proportional .to speed error, and the total flow `o'f-1iuidtothe cylinder 1| during off speedvwill be the summation of all flow dueto speed-error, were it not for the relief valves 19 capable of passing fluid around the cylinder 1| whenmanual-control of the blade angle-overrides fthev governor -control. The complete circuit of'iluid -floweto and -fromlthe cylinder 1| passes through the-cylinder 56 by means of the orifice 58, but'theorificeSS does not alter the amount of flow to the cylinder 1 I. #However the rate of flow of uidthrough the piston 51 by way of the orice 58 modifies Discharge through the orifice is somewhat limited, being less than that Lcapable-througheit-her passage 5,4 Vor 6|,.any movement of the piston 51 is resisted by one or the other of the springs 59 or 60, and flow into either end of the cylinder 56, builds up pressure, rst resistedonly vby the restricted orifice 58 andi-then theopposing one of High rates of flow to the cylinder 56 build up greater pressures than do low rates of ilow, wherefore movement of the piston 51 will vary with the rate of uid flow and the speed error. While equal unit volumes of fluid may pass through the distributing port of the valve 45 will in general effect equal movements of the piston 12, the displacement of the piston 51 may be otherwise, due to the rate of flow of those unit volumes, hence there is response to integrated speed error.

'Stability-'of governing action is eifected because,while vpiston 12 isl operating vto Agovern the engine by changingblade 'anglein-proportion to .cito give a spring, action,.piston51 is operating `to,give adequate damping of the system by changing the fuel rate (torque) .in .responseto f While refinements-of .this=natureihave not been necessary with the conventional reciprocating engine propeller combination, equally adequate system response in the case of systems using internal combustionturbinesihaving greatly increased effectiveiinertia referredto the propeller shaft axis requires increased rate of pitch change and vastly increased dampingwhich can most readily be effected through the fuel controlof the turbine as indicated in the foregoing. These refinements are particularly. necessary inthe case of the turbinefbecause of y'much greater 'susceptibility vto damage -by'overspeedin The-,damping means of the fuel `ratecontrol.positivelyv and immediately prevents :any serious overspeeding. :equivalent of thisaction cannot beobtained by `devices acting upon propeller pitch unless impractically `high rates of pitch ychanges are available :to counteract .sudden changes :in `fuel 8 centrali-settingsbythe-pilot. Iofkeepthe maximumfoversped downftoan acceptable valuecontrollerngand its linkages ltocam |34 and vthe .cam rise of|34 .will preferably 'be so proportioned that an overspeedas-,little as.1% ,willscausecontroller A :toffully -closeqa vfully ,open throttle.

Theroricej inthe,pst0n;51.represented diagrammaticallyinFig. 1,is.,a ftype of oriiice'which gives :a pressure :differential substantially in -proportion-to thefrst-:powenof-.the rate ofuow. vThe simple vorifice `"whichris shown :diagrammatically will give.substantially:tina-recuredefecty when the displacement -of1piston 51 is'relativelyggreat. vIn order `to obtainithe desiredseiect ;for'small piston displacemenupthe constructionzshown-n Figs. 18 to 2l=mayzbefnsed- .Piston 151' '(Fig. 18) carries azbushingi510 having hole 151| having the '.least diameter plasmid-section line :2 `2 0 Yincreasing to the greatestdiameters at .the Isidesof .the bushing 510. Hole 51| receives-wiping'512-Whichaisfcir- .cular ,inn-cross sectionat its .middle portion and whchisrprovidedwith ats i513 so'that the end views. of thefplug are that showniin'Figf21. yThe middleiportionof :theplugs l5.12 is `normally located .at `the.,sectionfline.-:20` at which :the hole 51| has Ythe smallest diameter,r said. diameter..be ing slightly greater than the diameter. of themiddle portionzoftheplug vas'slriown in1Fg.f1-8. Plug .512 -is attached tor aarod i514 loosely slidable through 'an-apertured plate 5.15 supporting the ends cf a leaf spring516-connected atits middle portion with the rod 514. ."I'he spring 516xresists displacementofthe plug '512 ineither direction fromthe normalpositionshown in.-Fig. 18. VWhen the 'conditionscausing displacement of the plug 512 from .normal -position cease, the spring 51.6 returnsthe plugzto normal position. As the rate offilow:offhydraulicffluidfthrough thehole 51| increases; the :area of :the -orice Lat .section line 2id-2c between ithezplug 51.2 andithe bushing '510 increases. Theshapeof :the plugr512is such that the difference between the* pressures on fopposite sideszofgthe-` piston :51"f'will 'be substantiallyA in proportion tothe tfirst power of the rate of flow N throughsaidforifce.

i.'.E'hezsilnple o rice58of Fig. 1 or the variable orice'of Fig. Y18 cansbe located'in parallel with the-piston ofcylinder'i'inpanymanner. For examplefeitherfof these orifices-maybe located vin a by-pass connecting the ends `of cylinder '56.

Theapparatusshown in Fig. 1 with the exceptionfof .the control lever 180, located inthe cockpit, can -beihoused ina single apparatusbox. The linirii` may be any :suitable vconnection between the controlilever:andrthecams-a-ndmay be a pushpull :cable located-'in a'guide tube. -In-'case the connectionsfrunning from-the control-lever to the apparatusbox lwere shot'away it might be desirabledto include in the :connections between the throttle andthe cams anon-reversing mechanism so ytlflatfthe .cams would remain inthe position la-.st'set Thiswmechanism may-be, for example, thatfshownrin-FigA. "Ca-blevor link (Fig. 1) is connected-withrthe rack 20|! meshing with a gear 20| ydriving a 'gearzmeshing ywith a gear 203 driving ,a gear 2M meshing with a gear -25. The liubfcfgear 2,55'is internally threaded to provide aznut'freceived by -a-threade'd shaft 206 whiclris connected with the. ca-msiml and H0.

v'Referring to Fig. 5, the cams 90, |00 and ||0 may beef the rotary1typein which case they wouldbemounted on-a shaftl2|9connected with -a'--worm vwheel2lIldriven'by Worm 2| 2 which Wouldbe driven `byrthegear lR15-of Fig. 4.

.':If the apparatus is tobe usedfor-asingle engine 9 installation, the synchronizing mechanism would be omitted, the omitted mechanism including the motor I8, the subtracting differential gears I3, I4, and I8, gear l1, pinion 20, clutch 2|, screw 22, nut 23, link 24, lever 25 and support 26. The shaft of pinion 23 would be supported by a yfixed bracket.

For a four-engine installation there would be four apparatus boxes each associated with an engine and each individually controlled by a control lever 80 as shown in Fig. 6. All four engines would be controlled by a master control lever 220 connected with a shaft-22| upon which each of the hubs 80a of the levers 33 are journaled as shown in Fig. 7. Each lever tit may be connected with the shaft 22| by placing the lever 80 in line with the master lever 220. When this happens, a detent ball 222 carried by the lever 80 is urged by spring 223 into a recess 224 provided by an arm 225 whose hub 225 is pinned to the shaft 22 I. The master lever 220, being frictionally connected with its quadrant 220 in any desired .position for controlling all four engines, one of the four engines may be individually controlled by moving its throttle lever 8B when the pilot wishes` to have an unsymmetrical thrust distribution on the plane for land or water maneuvering or wishes to feather the propeller on a disabled engine, etc. When any of the levers B0 are out of line with the master lever 220, such levers 80 are frictionally held against their quadrants 82 and will remain in whatever position they are located separately. Only those levers 80 which remain in line with the master lever 220 will be moved when the master lever is moved. `When those levers 80 which were moved out of line with master lever 220 are returned to position in alignment with lever 220, then those levers become connected again with the shaft 22| through vthe spring urged balls 222 connecting the levers 80 with the arm 225. Then the master lever 220 is operative to control all the engines.

Each of the levers 80 operates a cam 230 which is shaped so as to effect a speed of the threephase synchronous motor I9, Fig. 1, in conformity to the speed demanded by the speed setting cam Ilill. Each cam 230 engages a follower rollerl 23| supported by bracket 232; and all the brackets 232 are carried by a bar 233 urged upwardly by a spring 234 so that all of the followers 23| will tend to engage their respective cams 230. Bar 233 is connected by a link 235 with a lever 236 mounted on the crank throw 231 of la crank shaft 238 operate-d by lever 239 connected by link 240 in any suitable manner withall the cruise control levers 33 of the engine as represented in Fig. l. The movements of the lever 236 effect the control of the speed controlling unit 24| which determines the speed of a direct current motor 2li2 which drives a three-phase generator 243 which is electrically connected with all of the three-phase synchronous motors I9. When all of the levers 80 `are in line withthe master lever 223, movement of the master lever 220 causes all of the cams 230 to move togetheras one cam and to set the speed of the master motor 242 in conformity to the speeds demanded by the speed setting cams |00. This synchronizing system is however limited in its effect, owing to the limitation placed on the movements of the lever 25, Fig. l, by the stops 25a and 25b. Therefore when it is desired to control one or more of the four engines by moving its throttle lever 80 out of line with the master lever 223, the desired control can be effected. For example, if it is desired to have one engine operating faster than the others, the master synchronizer would be controlled by the lever` of that engine `and not by those levers 80 which remain in line with the master lever 220 since the position of the bar 233 is controlled by the follower 23|Vv calling for the highest speed setting. Therefore, when any of the followers 23| rides on the high part of the cam 230 the high speed operation of the synchronizer is set, although another of the cams 230 may be placed in position where its low land would be adjacent its cam follower. However, although the synchronizer of a particular engine would call for a high snychronous speed, the throttle lever 80 of that engine can move the cam 230 to a position calling for a lower speed. The result would be that there would be movement of the gear Il causing the pinion 20 to rotate, thereby causing movement of the lever 25 until it engaged one of its stops 25a or 25h. After that the screw 22 cannot rotate and the friction clutch 2| would slip while pinion 20 continues rotating. In addition to permitting operationA of one plant at a different speed, the limitation of synchronizing effect permits safe operation of `the power plants in the event of failure of the synchronizing system free of any serious, large increase or decrease in speed.

The apparatus provides for throttle control and pitch control in parallel. That is, these controls act simultaneously and in a, non-interfering manner. Therefore, constant speed control is assured in all flight and blade angle regimes to accuracy adequate to protect the prime-mover fuel rate) for the R. P. M., or vice versa. For

greater fuel economy at a given manifold pressure (or fuel rate), it may be desirable to decrease the speed setting. For this purpose the flight engineer may operate the lever 3B in a clockwise y direction, thereby elevating the rod 32 in order to reduce the equilibrium speed at the same time the synchronizer master speed should be similarly reduced. This is effected by the connection between the lever 36 of Fig. 1 and the lever 239 of Fig. 6 through the link 240. Movement of the lever 36 in order to reduce equilibrium speed causes lever 239 to move counterclockwise to drop the crank 231 lthereby dropping the left end of lever 236 for. a slower governed speed of the master motor 242. i

The throttle setting cam has its low portion r92 sufficiently low so that, even with the speed setting conditioned for its lowest value by the lever 36, fuel will need to be added by the throttle actuating cam |34 to maintain the idle R. P.,M. This is essential in rorder to keep the values low during idle and taxying conditions so that the limit cam ||0 will be able at angles near the gate values, to control propeller blade angle directly, both in positive and negative pitch. In the lower power regions the limit cam ||0 thus controls the follower roller 2| positively. This is desirable in this region where Q (torque) ll equalsornearly f equals 1zero; that is', the ratio'A is too small in valuefor` changein bla'deangleto effect any vappreciable lchange-in torque'.

Hereinafter, the A4 controllerI (Fig. 11) refers to the lpiston 5l and parts'connectin'gLA it with cam 136'; and theB 'controller refersto'th'eablade angle control servo iwhich is'controlled by the governor, and whose Aoperation maybe limited bycam I I0.

The transition gateof cam' H8' (between surfaces H4 and H5) may-'givezero blade angle or a slight negative bladeangle, for example, -4. Surface H8, which determinesy the low limits of positiveblade angle, extends `from the gate'to point H8"a which determines the lowest blade angle for Vfull power and speed'under hot day, zeroairspeed conditions. In' the positive range, surface HT sol limits 'upward-movement ofroller I'ZIaS-tolimit positiveblade anglelto themaximum required for high" speed divesfat full engine speedvr and power; or'- forcruising. Surface ||6 isla blocker; Roller |2512 cannotbe in` position to bereeeivediby 'tliegate-unless. air speed is low enough" for the-rollerv` |21 to-drop upon surface H8; Therefore shift 1 from posi'- tive-pitch to-negativepitch cannot be effected unless air speed has been suflioiently reduced. Surface H1; Whiehdetermines the low limits of negative blade angle, slopes from the gate-to point I Ha' whichdetermines the' lowest/'negative angle atl which full engine speed' can: be reached at the highest forward speedA of the plane that negative-thrust willbe calledfor at full power. This will givean angle which is appreciably more negative than the gatel in landing-run and even inV dive-braking vapplications.` In the negative range,` surface ||2 so limits downwardmovemen't of'roller |-2'| as to vlimitV negative blade angle to themaximum at which full=power-andrengine speedcan be developed understaticA conditions.l

The action off cam AH-Ii under different air speed conditions'will-now be described with reference'to Figs. 8-to 11.

In Figs. 8 to 1l, curves R90 and RA are plotted relative topositions of controlflever 80 in positive thrust range P, transition range Tand negative thrust range N. Curve -R'eu represents fuel rate called-for by theV throttle setting cam 90;

and curveRA represents fuelrate-required to maintain required engine speed for the minimum blade angle specified bycam H0 at the particular air speed' corresponding to the figure. Inv rangeT, between the right end G+ of'the gate and the `left end'G-of the gate, the curves become horizontal lines.

Figs. 8-10 are for 'anormal application requiring'braking only at landing-run'speeds.

Fig. 8 shows `the relation of curves Rat and RA for zero air speed. These curves cross at a: and y. To the right of 1:/ 4and to the-left of'x, curve R90 is' above Rie; and*v the horizontally` shaded portions indicate the-extent'to which camt calls formare fuel than isrequired toomain'- tain aselected vspeed'. These rangesv are Amarl-red cam 90'because vcam 9|)y determines the fuel rate which will give more speed than selected by cam |00,- and theA governor operates through controller Bite increasepitch in order to maintain the selected speed. Between'and-y, curve RA is above curveReo; andthe-vertically shaded portion indicated the-extent to which lcamv 90 calls for less fuel than is required-tov maintain a selected speed. This-range is marked A because cam 9|] demandsless fuel than required f2 to' maintain" thespeedselectedvby cam |00; and controllerfA operatesthrough cam |34 to.in' creasefthefuel rate in order to maintain selected speed.

Under zero air speed conditionsr surface v| |6is contacted by roller' |2| from the gate defined by surfaces H4, H5 to a point corresponding to point y of Fig. 8 as lever 80 is moved clockwise in the positiveV thrust range. Surface H8 is'so shaped that, duringv the positive portion of range A'- (Fig. 8), the B controller cannot reduce positive blade angle to such value that the governor willbe in equilibrium status. Therefore pressure fluid will ow in the direction of arrows marked underspeed to cause piston 51 of the A' controller to move left to effect downward movement of cam |34 to increase fuel rate in' order that required speed will be maintained by fuel rate increase'frather than by decreaseof positive blade angle.:

Ini 'tiiefn'egativepitch'l range, piston i2 moves up to' decrease negative pitch` and down' to increase negative pitch. Therefore surface H2V of cam HI) determines the' high limit ofi' negative pitch for various positions of lever 8U' in the negative pitch range. It permits the highest negative blade angle i. e. the angle required under'static conditions. Surface of cam |`|Il determines the low limit of negative pitch for various positions of lever 89 in the negative pitch range. Under zero air speed conditions, surface I'is contacted by roller |2| from the gate (defined by surfaces- H4, H5) up to a point corresponding to point :c of Fig. 8, as lever is moved counterclockwise in the negative thrust range. Surface is so shaped that, during the negative portion of range A (Fig. 8), controller B cannot reduce negative blade angle tosuch valuethat the governor will be in equilibrium status. Therefore pressure fluid will flow in the direction of arrows marked underspeed (valve 64 being reversed for negative pitch control), to cause piston 5T'of controller A to move leftv to effect downward movement of cam |3l'to' increasefuel rate in order that the required speed will be maintained by fuel ratevincrease rather than by decrease of negative blade angle.

Although cam surfaces ||`8 and IH may block movements of piston 12 of controller B down and up, respectively, pressureeuid now continues in the manner'stated because, when piston l2 stops, one of the relief valves'19 opens.

Fig: 9 shows curve R90 and curve RA for 120 M. P'. H. air speed.' 'Io-theleft of intersecting pointe,A the-'A-controller isactive to determine the-'fuel'rateV To the right Aof point z, the fuel rate-is=determinedby'cam 90, the A-controller acting momentarily, only as required to stabilize the governing. As the cam H0 is moved right from positive thrust position, roller |2| isabove cam surface H8 until a position of cam Hoi is reached vcorresponding to point a of Fig. 9. Then roller |2`| engages cam surface H8. Thereafter roller. |2'|fo1lows cam surface |21l to the gate andcamsurfacel to point IHa. To the left ofpoint z, the vertically shaded area shows thezdeficien'cy in the'fuel rate called for by cam Swhichis made up by the operation of controllerA. To the right of point e, the horizontally shaded areafshows tlreiexcess of fuel rate demanded byY cam Sllwhich requires the governor to increase bladeangle vin order to prevent exceeding the selected speed. The latter lshaded area is greater than area to lthe right of point y;of Fig.

8, because less power from the engine is required, at 120 M. P. H. air speed than at zero air speed, to turn the propeller at the required R. P. M. in positive pitch.

Fig. 10 shows the relation of curves R90 and RA for 300 M. P. H. air speed. At this air speed, RA is mostly below the zero power line, thus denoting that propeller windmills the engine. As indicated by the large horizontally shaded area, the fuel rate represented by Rao is much in excess of that required to maintain the required engine speed. Hence the governor is demanding` high positive blade angles. Roller I2I, being substantially above cam surface IIE of cam (Fig. 1) under these conditions, is not in position to be received by the gate (defined by surfaces II4, H5) but blocks movement of cam Il() to the right by engaging the surface |I6 of cam IIB. Hence the curves R90 and RA are shown by the dotted lines to the left of gate entrance denoted by line G+. Surface II6 being a blocker, air speed must be reduced to a value such that roller I2| will engage surface |I8 before lever 80 can be moved into a negative thrust position, as is required if overspeeding is to be avoided.

Fig. 11 shows curves R00 and RA and R'A when the apparatus is modified for dive-braking. For dive-braking applications, grooves 0I, 92 and 93 of cam 90 are changed as indicated in dot-dash lines (Fig. 1) at 9|', 92 and 93' respectively. This provides such lowering of the fuel rate, in the ranges of low positive and negative thrust positions of lever 80, that there is a tendency of prime-mover speed to fall below required speed even when air speed is high, for example, 300 M. P. H. when the prime-mover is a turbine, Lor 200 M. P. H. when the prime-mover is a reciprocating engine. Therefore the governor will attempt to reduce positive blade angle in the low positive thrust position of lever 80 and to reduce negative blade angle in the low negative thrust position of lever 80. Surfaces H8 will engage roller I2| and guide it into the gate and surface III will receive the roller |2| as the gate passes to the right from the roller. In this way, the shift from positive to negative blade angle can be made at relatively high air speed. During this transition period, the A-controller determines fuel rate in order to maintain required speed. If

cam II I were used for dive-braking applications,

the A-controller would be effective, during negative thrust, to give the fuel rates indicated by dotdash line curve RA. This curve reaches 100% power value before the lever 80 reaches full negative thrust position and further movementy of lever 80 would force the power plant to drop in speed at this high forward speed. To avoid this, cam surface I I I is changed to I I I; and control according to line RA is obtained. To the left of point w, when R90 crosses RA, controller A is effective to give the speed required.

The controller apparatus may be used with various types of propeller hubs having a blade pitch changing unit assembled therewith, for example, the hub and torque unit assembly shown in the patents to Blanchard and MacNeil, Nos. 2,307,101 and 2,307,102 issued January 5, 1943. Fig. 12 shows somewhat diagrammatically a propeller hub and torque unit assembly of the type disclosed in these patents. From the engine frame 300 there extends an engine driven shaft 30| which supports and drives a propeller hub 302 which supports an accumulator 303 containing a piston 304 movable toward the right from the position shown under the action of com- `l4 pressed gas forced into the accumulator through a check valve'305. The space, between the piston 304 and the xed wall 306 of the accumulator, receives oil under pressure which forces piston 304 toward the left further to compress the gas to the left of the piston, thereby maintaining a supply of oil under pressure for the purpose of feathering and unfeathering the propeller blades. Duct 301, through which oil flows into the accumulator, is controlled by a valve to be described.

The hub 302 supports a plurality of blades 3|0, each having its root journaled in bearings 3| I. Each blade is rotated about its root axis by separate torque unit comprising a cylinder 3I2 attached to a blade root and having its upper end closed by cap 3| 3 and rotatably supported at its lower end by a bearing 3|4. Cylinder 3| 2 cooperates with a piston 3I5 having external helical splines 3Ii6 cooperating with internal helical splines 3I1 of the cylinder 3I2 and having internal helical splines cooperating with external helical splines 3I8 of a relatively fixed member 3|9 supported by the hub 302. Pipes 320 and 32| lead respectively to the inner and outer ends of the cylinders 3| 2 and are connected in a manner to be described with a distributing valve. The spiral splines are so constructed that inward movement of the piston 3I5 effects rotation of the cylinders 3|2 (clockwise looking outwardly) for the pitch increasing function; and outward movement of the pistons 3I5 effects rotation of the cylinders 3I2 in opposite direction for the pitch decreasing function. The cylinders 3| 2 are each connected with a bevel gear segment 322, each meshing with a master gear` 323 supported by a bearing 324 carried by the hub 302, thereby equalizing the pitch changing movements of the blades.

The hub 302 supports a plate 330 which, as shown in Fig. 14, is secured by'tubular nut 33|. The plate 330 and its cover 332 (Fig. 12) provides a reservoir for hydraulic fluid.r The kengine shaft 30| is surrounded by a non-rotatable tube 333 concentric with the shaft and with the nut 33| (Fig. 14). Tube 333 is provided with a tang 334 (Fig. 12) received by a notch between brackets 335 attached to engine frame 300. The plate 330 and its cover 332 provide bearings which maintain the concentricity of the tube 333, one of these bearings being shown at 336 in Fig. 14. Each bearing has a seal such as 331. Tube-333 provides an annular flange 338 which supports a plurality of shafts 339 each driven by a pinion 340 meshing with a ring gear 34| rotatably supported in any suitable manner by the sleeve 333. Ring gear 34| is operated by shaft 11 (Fig. 1) through any suitable mechanism such as a pinion 342 driven by shaft 11 and meshing with the gear.

Obviously, rotation of shaft 11 by controller B effects rotary movements of shafts 339 for the purpose of obtaining blade pitch change. Each shaft 339 provides a screw 345 threaded into a grooved ring 345 slidably along the tube 333. Ring 346 receives a shoe 341 (Fig. 13) attached to ra rod 34B guided for movement parallel to the .the gears 380,' 382 andv 335.

nected byannular rgrooves-364.1363 and-358cm- .spectivelywith holes39, 310. and 31 respectively. 'Hole 310 is connectedin a mannerto bedesoribed with a pressure pump. Hole 35S` 'is connected with passages 32| and hole. 31| is connected with Vpassages 32B.

The position. of valve3l. is determined bythe position .of carriage;354-which 'carries a roller 312 engageablewith alever313 4pivotally supported by pin 314 carried by a screw 315 attached to the valve body. 358. '.Lever313 is provided with a notch 316 receiving a pin 311. attached' to the valve 36|. YSince centrifugal force vacts upon the valve'35l as indicated by arrow 36 I a, Fig. 14, the lever 313 remains inengagement with the roller 312 while the propeller hub is rtated. Hence, no spring is required to -hold the lever 313 against the roller 312. When piston 12 of the controller B of Fig. l moves up to demand pitch increase, shaft 11 rotates counterclockwise as viewed from the 'right in Figs. 1 and l2. Hence, the gear 34|, 'the pinions 340, the shafts 339 rotate in the same direction thereby causing'the grooved ring 345 vto move toward the left, thereby moving the. carriage 354 toward the left. .As

roller-.312 moves toward the left centrifugal force causes the valve 35| toA move upwardly thereby tatedr about theirl root axes vin the .direction of -pitch increase,1the valver36| is vbeing returned to a balanced Aposition closing ports 363 and'351 at which position the valve arrives when the demand for pitch increase has been satised. In order tovv accomplish this, 4the .master bevel gear 323 is connected'with a gear'330 CFig; 16) which is retained by a plate 33| attaohedto the hub 332 and which meshes with a-gear332 vpivotally supported by a screw 383' attached to a lplate 364 supported by hub 362. `Gear :382 meshes with gear 385. attached to a shaft having a .bearingand a boss 381-integral withthe` plate 334. Shaft' 386. is connected with .a coupling disc388 connected by a screw 383 with av coupling disc 330 attachedv .to a shaft 39| journaled. in a bearing 392 carried by the Vplate 333 and retained by anut 393 threadedon the bearing 3S2-as shownin Fig.

`16. Shaft 39| is providedv with a .helical groove 395. which receives a ball 393 carried by a member3391 which serves as a .nut and travels .along fthe helical. or screw-threaded groove`395. Nut l391 provides a vstud 398 passing through a slot 399 ;bossi 381 and the other end received bynotchx403 4in the hubof 'thecoupling disc'38. The spring `4J| is initially wound up-in order tosprng-load Coupling screwA 389 passes through an elongated arcuate hole 39Go. in .the disc 390, thereby providing for angular .ad- .iustment between. the coupling discs 388 ,and 390.

When carriage1354` is inthe position shown in Fig. 14 and -in full section lines .'(Ffigl) the valve V36| is in neutral position blocking ports 353 and '361 so that the torque units will not operate. One

set of conditions which places valve'. 35| in neutral position, is that which exists when screw 3.49 and stud A393 are located asshownin Fig. 15. These are the conditions for minimumpositive-or.maximumnegative pitch. To'decrease thepitchnegpositively,

,fleftf from 4the position shown-infig 14. VrThe demandv forypitch increase, positively, Vmay be such in position 350 and carriage 354 in position, 354' (Fig. l5). This Willfeect blade angle increase, in the manner described. During blade angleincrease, the mastergear 323 rotates counterclockwise as. indicated by arrow 3231i in Fig. l2 or clockwise in Fig. 17 as indicated by arrow 323i). Therefore the shaft 363 will rotate clockwise in Fig. 17,'v thereby causing the screw 385 to rotate counterclockwise as indicated br arrow 39501. when viewed from the direction of arrow 3951i (Fig. 16). Therefore, while the .blades are being rotated to increase pitch, the nut 391 will be moving .down in Figs. l5 and 16 thereby carryingk the stud 398 to the position .398 which causes the carriage 354 to be brought back vinto position shown in full lines in 15 thereby returning the valve 36| inbalanced position. If the movenientof ring 346 hadv been such as to 354 thereby demanding a greater blade angle change rwhich would cause the stud 398 to move .to 338 before the valve 360 is returned to balanced position. It is therefore apparent that for every position of the ring 346, there is a definite blade angle. Consequently, there is a definite blade angle position for every position of the piston 12 of the controller B of Fig. l. The mechanism shown provides for adjustment of blade angle in a range of approximately The ilange 338 oi sleeve 333 (Fig.112) provides a stationary gearf4|0 meshing with a gear 4|| which drives a pumpv'llwhilev the propeller hub is rotating. Theoutlet of. pipe p of pump P is connectedwith the passa-ge 31D of the distributing valve 350. Pipe p' is connected by pipe p1 lwith a pressure control lunit PC connected by pipe p2 with an accumulatorvcontrol valve unit AV. The pressure control unit PC comprises a valve rod 43D having a dashpot head. 43| received by a cylinder. 432 connected with pipe p1. Rod 430 urged outwardly by centrifugal force acting inthe direction of arrow 433 and by spring 434 in opposition to `fluid pressure acting upon the lower (in Fig. 12)-surface of a piston valve 435 received by a cylinder. 435and controlling a relief port 431. The inner `encl of cyiinder 436 is connected by pipe 438 with pipe 32|. Valve 435,

'being responsive to centrifugal force, causes the pressure in line p to increase as speed increases and this pressure is increased also when cylinder '436 receives pressure from the pipe 32| which is minimum value by movement of rod 440 to a po- .s1t1on for connecting the ports 431 and 443, valve 435` having opened port 431. Up to a certain rotative speed of the hub, the pressure is limited to -a minimum value in orderl that the accumulator ywill 'befully charged within a short timey even while the engine is operating at low speed. This vminimum pressure -is suiicient -for the pitch-decreasing function of the torque units. As propeller speed increases, valve 435, being under control by centrifugal force, requires greater line pressure to cause the opening of the port 431. Therefore the pressure increases in pipe p above the minimum in order to make available the pressures required for the pitch-increasing function which requires greater pressure with increase of speed.

While rod 44B of unit PC is shown parallel with rod 430 which is under the action of centrifugal force, it will be understood that rod 44D is not controlled. by centrifugal force but is actually located at right angles to rod 430. The units PC and AV are fully described in the copending application of David A. Richardson, Serial No. 613,56'3, filed August 30, 1945.

For the understanding of the present invention, it is sufficient to state that the accumulator control valve unit AV has a check valve 450 which normally blocks fiow from the accumulator 3D3 to pipe p1. When feathering is required, ring 345 is moved to the extreme left to cause a roller 451 (carried by a sho-e 452 received in the groove of ring 345) to engage cam 453 on a lever 454 and to effect outward movement of said lever and of a rod 455 thereby opening the check valve 45:1. Pressure oil then flows from the accumulator to underside (in Fig. 12) of a piston 456 thereby effecting the opening of a valve 451 so that the accumulator may discharge to pipe p1 through a by-pass around the check valve. During this discharge the valve 451 is held open by oil pressure against the underside (in Fig. l2) of a piston 458. As feathering is completed, the pressure differential between the pressure in pipe pi and the pressure against the underside of piston 458 decreases and spring 459 closes Valve 451. Cam 453 having been momentarily contacted by roller 45| during movement of ring 346 to the extreme left, check valve recloses. Therefore discharge of the accumulator is prevented until it is desired to use accumulator pressure to assist in the unfeathering operation. This is effected by right (in Fig. 12) movement of ring 34S Which effects momentary opening of check valve 450; and discharge of the accumulator into pipes p1 and D takes place.

The pilot may over-ride the B-controller (Fig.

1) by operating lever 5GB (Fig. 12) connected by link 50| with arm 562 provided by ring gear 341.

Summary The apparatus for governing the speed of the prime-mover has inherent stability because it includes instruments which are respectively sensitive to fp (displacement or integrated speed error) and to p (rate of displacement or speed error). The instrument sensitive to adjusts the torque absorbing ability of the Work-device (propeller) operated by the prime-mover. The instrument sensitive to tp adjusts the medium (fuel) which causes operation of the prime-mover. Both in struments operate jointly during the normal operating range of the prime-mover to effect a stable governing action.

In the application of the governing apparatus to a primemover-propeller power plant, the instrument sensitive to qi operates to change bladepitch in proportion to qb and at a rate proportional to qb, amount of speed error. The .instrument sensitive to p operates to effect a deviation @of fuel rate from normal (as set by cam 90). Hence the rate of deviation of fuel rate from normal is proportional to or rate of change of speed error. For example, if the prime-mover starts to overspeed, blade angle starts to increase at a rate proportional to the amount of speed error. This increase is accompanied by a decrease of fuel rate, from the rate set by cam 90, at a rate which Iis proportional to the rate of change of speed. The decrease in fuel rate has the effect of lowering the maximum of the speed error at which instant the blade-angle is being increased at the maximum rate. As speed error falls, the rate of blade-angle increase diminishes and the fuel rate is caused to increase to the normal rate set by cam 90. The rate of fuel-rate increase toward normal is proportional to the rate of de` crease of speed error toward the governed speed set by cam H30. By the time blade-angle has been increased to give zero speed error, the de-- viation of fuel-rate from normal Will be zero in the case of the use of a degree of stabilization equal to or greater than the critical, amount. There is a temporary modification of fuel-rate for the purpose of securing stability; but the fuelrate returns to normal when that purpose has been accomplished.

Errors have been substantially eliminated because there is a common zero for the 1s-sensitive instrument B and the qi-sensitive instrument A; and there is a common operating medium for these instruments. The common zero is established by the speed controlled valve (parts 45, 4S and 4.1); and the common operating medium is the pressure fluid which actuates instruments A and B when this valve responds to speed error.

The speed responsive governor valve controls rate of iiuid ow in proportion to the amount of off-speed. Hence the apparatus provides an hydraulic flow proportionalizing governor. It feeds pressure iiuid to the servo-motor, instrument B, the displacement of whose piston is a measure of rp. It feeds pressure fluid to the orifice 58 of the piston of instrument B. vThe pressure differential across the orifice 58 furnishes a measure of This orifice 58 and the linkage system to cam |34 is so proportioned as to give the desired degree of stabilizing action to the complete system. The degree of-stabilization may be the critical amount in which case there would be only one oscillation of speed error from zero to maximum and return to zero. Usually the practice is to use a degree of stabilization less than critical since equilibrium is substantially established in less time than with the critical amount altho there would be a few additional slight oscillations of speed error before return.

to zero.

The governing system is well-adapted -for use with a prime-mover having relatively high effective inertia such as the internal-combustion turbine which 'is desirably operated at high R. P. M. throughout the full operating range. The necessary governing action is effected Withoutrequiring blade angle change to be made at impractically high rates because the temporary fuel-rate modification helps to maintain the maximum speed error within safe limits while blade angle is being changed at a practical rate.

'The apparatus provides means for controlling the engine-propeller power plant to effect the desired engine speed and power during all positive and negative thrust operating conditions.v

This means is under control by a single main con.- trol lever which operates ina desired range'of negative thrust and in a desired range of positive l 9 thrust including feathering. The control means provides for direct manual control of blade angle during relatively low blade angle conditions when is practically zero. Blade angle` can be set manually by the main control lever to the proper value for starting the prime. mover.

The apparatus provides a. manually operated, continuously variable control from highest negative thrust to highest positive thrust. By means of a single control lever, fuel-rates and engine speeds are selected according to a predetermined schedule of positions of the lever in the. positive and negative thrust ranges and values of iue1-rate and engine-speed. In normal forward flight. the control is effective according to the schedule determined by cams 90 and |00 and the selected speed is governed by automatic change in blade angle by instrumentv B accompanied by the stabilization effected by instrument A. At relatively low blade angles, particularly under static conditions, speed is approximately determined by cam |00, While blade angles are determined by the manual setting of cams H0 or III. Under these conditions, blade-pitch cannot be reduced, positively or negatively, to such value as to actually maintain the speed called for by cam |00, in consequence of which instrument. A is caused to function to increase the fuelrate above that scheduled by cam 90 in order to maintain a necessary speed altho slightly less than called for by cam |00,

Unless manual control blade angle is effective, movement of cam plate I0', and therefore, lever 80 cannot be moved from the. positive thrust range to the negative thrust range; and, therefore, the transition from positive thrust to negative thrust cannot be made under high air-speed conditions excepting in case the control is modin'ed for dive-braking as explained with reference to Fig. 11.

The. cam plate I0 provides for manual control of blade angle for feathering;

T'hev apparatus provides for modi'cation,v in a limited range, of the speed setting by cam |00 by means controlled by a synchronizer. Therefore, in case ofl a multi-engine application, minor adiustments of speed of each engine can be made byv the synchron-izer. Synchronization is effectible throughout the positive and negative pitch range of each engine.

In the case of a multi-engine application, each lever 80 operating the control apparatus of each engine controls the synchronizer in conformity to the control of speed by cam |00. All of the levers 80 may be controlled by a master'lever 220; butY each lever 80 may be independently operated to obtain a speed outside the range of the 'synchronizer for land or water taxying purposes.

For cruising purposes, the apparatus of each engine providesl for modification of the speed settingby cam |00 by a: lever 36'. In the case. of a multi-engine application, all, of the levers 36 are operated by a single lever C which alsocontrols the synchronizer'in order to reduce synchronizer speed for cruising purposes.

While the, embodiments of the present invention as herein disclosed, constitute a preferred farm, it is. to be understoodthat other forms mightbe adopte.d, rall coming within thescope of the. claims which follow-.

What is. claimed is as follows:

1.. A prime-mover speed-governing system comprising a work or torque-absorbing device operated by the prime-mover, a device including a fluid pressure servo having a pilot valve and follow-up piston for' controlling the operating medium of the prime-mover, means including a fluid actuated piston sensitive to integrated speed error for varying the torque absorbed by the work device in orderl to eliminate a speed error, and stabilizing means including a damped piston servo sensitive to speed error for controlling the device which controls. the operating medium.

2. A prime-mover speed-governing system comprising av Work or torque-absorbing device operated by the prime mover, a device including a. fluid pressure servo having a pilot valve and follow-up piston for controlling the operating medium of the prime-mover, means including a. fluid actuated piston sensitive to integrated speed error, means including a damped piston servo sensitive. to speed error, a ymechanism including a.v selectable speed setting member under control by said rst means for controlling the tormneabsorbed by the Work device, and a mechanism under control bythe other of said means i or actuating the device which controls the operating mediuml 3. A prime-mover speed-governing system comprising a Work or torque-absorbing device operated by the prime mover, a device including a fluid pressure servo having. a pilot valve and follou -up piston for controlling the operating medium ofthe prime-mover, a pressure-fluid source, a speed responsive valve closed when the primemover is on speed and opening when the primemover is off-speed to permit a flow of pressure luid from the source,v means including a fluid actuated piston actuated in proportion to integrated speed error by said flow, means including a damped piston servo actuated in proportion to speed error by said flow, a mechanism under control by saidv second means for controlling the torque absorbed by the work device, and a mechanism under control by the other of said means for actuating the device which controls the operating medium.

4n A prime-mover speed-governing System comprising. a. work. or torque-absorbing device operated by the prime-mover, a device including av fluid pressure servo having a pilot valve and follow-up. piston for controlling the operating medium of the prime-mover, a pressure-duid source, a speed responsive valve closed when the prime-mover is on speed and opening when the prime-mover is oil speed to permit a flow of pressure duid from the source, means including a. duidactuated piston actuated in proportion to integrated speed error by said flow, -means including a. damped piston servoI actuated in proportion to speedl error by said flow, a mechanism including a selectable speed setting member operated by theA nrst means for varying. the torque absorbed by the work device in order to eliminate a speed error and a mechanism including a rate of fuel valve operated by the second means for actuating the device which controls the operating medium whereby stability of governing action is effected.

5. In a speed-governing system for a primemover and propeller power-plant, the combination comprising, means for adjusting the angle of the propeller blades according to a certain setting, a pressure fluid source, a distributing valve comprising; a. valve-body' having an inlet port connected with. the source and distribution porta a' movable speed-responsive valve element for controlling the distribution portsin accordance with over-speed or under-speed, a servomotor having a piston enclosed by a cylinder whose ends are connected, respectively, with the distribution ports, one of said distribution-ports being a discharge port for one end of the cylinder when the other end of the cylinder receives pressure-fluid from the other of the distribution ports, a mechanism operated by the piston for setting the blade angle adjusting means in order to eliminate a speed error and fluid pressure operated means Iactuated by flow of fluid in a connection between the cylinder and one of the distribution ports for controlling the operating medium of the prime-mover in order to eiect stabilization of the governing system.

6. A prime mover speed control system comprising a member for controlling operating medium input to the prime mover, manual operable means for controlling said member, a work or torque-absorbing device operated by the prime mover, a prime mover speed responsive governor, means including a fluid actuated piston under control by said governor and sensitive to integrated speed error for varying the torque-absorbing ability of said device, and means including a fluid pressure servo having a pilot valve yand follow-up piston under control by said governor and sensitive to speed error for adjusting said member independently of the manual control of said member.`

'7. A prime mover speed control system comprising a member for controlling operating medium input to the prime mover, manual operable means for controlling said member, a work or torque-absorbing device operated by the prime mover, a prime mover speed responsive governor, means including a fluid actuated piston under control by said governor and sensitive to integrated speed error for varying the torque-absorbing ability of said device, means including a cam and follower connected to said fluid actuated piston for limiting the action of said first means to reduce the torque-absorbing ability of said device whereby the demand by the governor for reduced torquev is unsatisfied, and means responsive to the unsatisfied demand by the governor for torque reduction for adjusting said member independently of the manual control of said member.

8. A prime mover speed control system comprising a member for controlling operating medium input to the prime mover, manual operable means for controlling said member, a work or torque-absorbing device operated by the prime mover, a prime mover speed responsive governor, means including afluid actuated .pistony controlled by the governor and sensitive to integrated speed error for controlling the torque absorbed by said device, means including a cam and follower connected to said iiuid actuated piston for limiting the action of said rst means to reduce the torque-absorbing ability of said device whereby the demand by theA governor for reduced torque is unsatisfied, and means including a damped piston servo under control by the governor for adjusting said member independently ofthe manual control of said member, said last named means operating in response to speed error when the second named means is not functioningand said last named means operating, when the second named'means is functioning, in response to the unsatisfied demand by the governor for reduction in the torque yabsorbed by said device.

9. In a control system for an aircraft power plant including a prime mover and a propeller driven thereby having variable pitch blades, said system comprising a governor driven by the prime mover and having speed setting means, means sensitive to demand by the governor for adjusting blade angle to maintain the speed for which the governor is set, said means including an element, the position of which determines the blade angle, a member for controlling the operating medium of the prime mover, a manually operable main control lever for controlling prime mover speed and power, said lever being movable in positive and negative ranges of control, cams operated by said lever in both ranges of control respectively for adjusting said member and said speed setting means in order to obtain prime mover power and speed in both ranges according to a predetermined schedule, means operated by the lever during movement between said ranges of control for conditioning the blade angle adjusting means for positive pitch control when the lever is in the positive control range and for negative pitch control when the lever is in the negative control range, and means positioned by the lever in either range of control for limiting movement of said element by governor action to certain maximum and minimum values of blade angles.

l0. In a control system for an aircraft power plant including a prime mover and a propeller driven thereby having variable pitch blades, said system comprising a governor driven by the prime mover and having speed setting means, means sensitive to demand by the governor for yadjusting blade angle to maintain the speed for which the governor is set, said means including an element, the position of which determines the blade angle, a member for controlling the operating medium of theprime mover, a manually operable main control lever for controlling prime mover speed and power, said lever being movable in positive and negative ranges of control, cams operated by said lever in both ranges of control respectively for adjusting said member and said speed setting means in order to obtain prime mover power and speed in both ranges according to a predetermined schedule, means operated by the lever during movement -between said ranges of control for conditioning the blade angle adjusting means for positive pitch control when the lever is in the positive control range and for negative pitch control when the lever is in the negative control range, a cam contactor connected with said element, and a cam operated by said lever and having a gate forreceivmg the contactor as the levermoves fromv the positive range to negative range of control, thev ends of said gate leading into spaces between cam surfaces which are engageable by the contactor for the purpose of limiting blade angle adjustment by the governor to certain maximum and minimum limits in both ranges of control.

11. In a control system for an aircraft power plant including a prime mover and a propeller driven thereby having variable pitch blades, said system comprising a governor driven by the prime mover and having speed setting means, means sensitive to demand by the governor for adjusting blade angle to maintain the speed nfor which the governor is set, said means including an element, the position of which determines the blade angle, a member for controlling the operating medium ofthe prime mover, a manually operable main control lever for controlling prime mover speed 23 and; power., said lever being movable in positive and negative ranges of control, cams operated by said lever in both ranges. of control respectively for adjusting said member and said speed setting means in order to obtain prime mover power and speed in both ranges according to a predetermined schedule, means operated by the lever during movement between said ranges of control for condittoning: the blade.v angle adjusting means for positive pitch con-trolwhen the lever is. in the posit'n control range and for negative pitchl control when the; lever in. the negative control range, a cam contactor connected with said element,y and a cam operated by said lever and. having a gate for receiving the.` contacter as. the lever moves the positive range to negative range of control, said camy having surfaces for guiding the. eontactor into. the gate and for providing limita.- tons on governorv enforced movements of said element.

I2. In a control system for an aircraft power. plant. including a prime. mover and a propeller` driven thereby having variable pitch blades, said system. comprising a governorY driven bythe prime mover and having speed setting means, means sensitive to demandby the governor for adjusting blade angleto maintain the speed for which., the governor isset, said' means including an element, the position of which determines the blade; angle, a member for controlling the operating medium ofV the prime mover, a manually operable main control lever for controlling prime mover speed and power, said lever being movable. in positive and negative ranges of con-trol, cams operated by said lever in both ranges of control respectively for adjusting said member and said speed setting means in order toI obtain prime moverl power and speed in both ranges according to. a. predetermined schedule, means operated by the` lever during movement between said ranges' of' control'4 for conditioning theblade angle adjusting means for positive pitch control when the lever is in the positive control range and for negative pitch control when thelever is in the negative control range, a camcontactar connected; with said ele-V ment, and a cam operated' byr said lever andf havingfa gate vfor receiving the contaetor as the lever n'rovesv from the positive range tonegative range ci" control', said: cam havingfa surface forr guiding the contacter into the gate as the lever moves from. the positive thrust range toward' the nega-- tive thrust range of' control and having a surface engageable bythe contactor in order to prevent movement of the lever into the negative thrust range under relatively high blade angle condi'- tions, thereby requiring reduction of air speed so thatv the. contactar may be caused, by operation o1' the governor, to contact the; guiding surface.

13. A prime mover control system for. use in dive braking comprising a member for controlling the. input of operating medium to the prime mover, a propeller driven by the prime mover and having variable pitch blades, a prime mover driven governor, means sensitive to demand by the governor for adjusting the blade angle to maintain. the speed for which the governor is set, said means including an element, the position of which determines the blade angle, a contactor connected with said element,y a control lever movable inthe. same. direction from maximum to minimum in a, range of positive tbrustdnv a range of. transition. from minimumV positive thrust. to negative. thrust and from. minimum. to in a range, of` negativel thrust, a cam operated by the. lever andv having a gate. for receiving the. contacter as the, lever moves in4 its. transition. rangev and having a cam surface. for guiding the contactor into. the gate, as the, cam moves from positive range into the transition range,l means operated by the. lever. for controlling the inputl of operating medium to the prime moyen and means operated by the lever for adjusting the speed setting` of the governor, the means for controlling operating medium being constructed to reduce input of operating medium so that, under dive brakingconditions, the contaeter. will be. engaged by said cam surface and will be guided into the gate` as the lever moves the cam from. the positive; thrust range into the transition range..

1.4.v In a system, of control for a prime-moverpropeller power-plant, the. combination com,- pi-1sing,4 a member for control-ling the operating medi-um of the' prime. mover, a propeller blade adjusting. mechanism, av speed responsive governor operated by the prime mover, a source of. flu-id pressure, a valve for distributingv fluid flow-v from said source having a pressure port connected-with said source and a pair of control ports., a valve element operated byy said governor for controlling the flow of fluid through said control ports, a. servomotor having a cylinder and piston, said cylinder having` chambers which are connectedto said control ports, saidpiston being movable in response to the fluid flow' con-- trolled by said. governor operated valve element for operating the bladeA adjusting mechanism to ccrrect.- a speed error, a second servomotor having a, cylinder and av damped piston, passage means connecting opposite,- sides of the. damped piston to enable. iiow of fluidbetween. the valve element. and the first recited servornotor,` said cylinder of the second servomotor having chamberswhich are connected to said control ports, said dampedpiston being movable in response to fluid flow controlled by. said governor operated valve` clement for. adjusting said operating medium control member during an off-speed condition, and coordinated manually. operated devices. respectively for adjusting said member and for. adjusting. said governor to obtain operating medium input and prime mover speed according. to a predetermined schedule, said damped piston having linkage connected thereto for effecting.. control of. saidA operating medium control. member independently of the setting of the manually operated device which adjusts said' member.

1,5.. In a, system, of. control for a prime-moverpropeller power-plant,l the combination comprismg, a member for controlling the operating medium of the primemover, a propeller blade adjusting, mechanism, a speed responsive governor operated by the, prime mover, a source of fluid pressure, a valve for distributing fluid flow from said. source havingA a pressurev port connected with., said source. andA av pair of control, ports, a valve, element operated by said governor for. controlling the ow of fluid through said control ports, a` servomotor having a, cylinder and piston, said cylinder having chambers which are connected to said control ports, said piston be.- ing movable. in response to the. fluid flow controlled by said governor operated valve elementV for operating. the., blade. adjusting mechanism to, correctA a speed error., a second servomotor hav-v ing a, cylinder and a. damped piston, passage means connecting opposite sides of the damped piston to enable ow of uid between the valve element andthe first recited servomotor, said cylinder of the second servomotor having chambers which are connected to said control ports, said damped piston being movable in response to liuid flow controlled by said governor operated valve element for adjusting said operating medium control member during an off-speed condition, coordinated manually operated devices respectively for adjusting said member and for adjusting said governor to obtain operating medium input and prime mover speed according to a predetermined schedule throughout positive and negative thrust ranges, and a manually operated valve in the connections between said control ports and said cylinder chambers for conditioning said servomotors for negative pitch when said devices are actuated from the positive thrust range into the negative thrust range, and vice versa, said damped piston having linkage connected thereto for eFecting control of said operating medium control member independently of the setting of the manually operated device which adjusts said member.

16. In a system of control for a prime-moverpropeller power-plant, the combination comprising, a member for controlling the operating medium of the prime mover, a propeller blade angle adjusting mechanism, a speed responsive governor operated by the prime mover, a source of iiuid pressure, a valve for distributing fluid flow from said source having a pressure port connected with said source and a pair of control ports, a valve element operated by said governor for controlling the flow of fluid through said control ports, a servomotor having a cylinder and piston, said cylinder having chambers which are connected to said control ports, said piston being movable in response to the fluid flow controlled by said governor operated valve element for operating the blade angle adjusting mechanism to correct a speed error, coordinated manually operated devices respectively for adjusting said member and for adjusting said governor to obtain operating medium input and prime mover speed according to a predetermined schedule in a range from zero to highest thrust, manually operable means effective in the low thrust range for limiting movement of said piston independently of said governor operated valve element whereby the blade angle Vvice whereby an operating speed is maintained.

17. In a system of control for a prime-moverpropeller power-plant, the combination comprising, a member for controlling the operating medium of the prime mover, a propeller blade-angle adjusting mechanism, a speed responsive governor operated by the prime mover, a source of fluid pressure, a valve for distributing fiuid now from said source having a pressure port connected with said source and a pair of control ports,v a valve element operated by said governor for controlling the flow of fluid through said control ports, a. servomotor having a cylinder and piston, said cylinder having chambers which are connected to said control ports, said piston .being movable in response to the fluid ow controlled by said governor operated valve element for operating the blade-angle adjusting mechanism to correct a speed error, a second servomotor having a cylinder and a damped piston, passage means connecting opposite sides of the damped piston to enable flow of iluid between the valve element and the first recited servomotor, said cylinder of the second servomotor having chambers which are connected to said control ports, said damped piston being movable in response to fluid ilow controlled by said governor operated valve element for adjusting said operating medium control member while the correction of blade angle is being made for effecting stabilization of the governing function, manually operable means eiective in the lower range of blade angle for limiting the movement of said rst mentioned piston independently of said governor operated valve element whereby the blade-angle adjusting mechanism is unable to decrease the blade angle an amount demanded by the governor to eliminate under-speed, said damped piston having the means connected thereto for actuating the operating medium control member to increase the input of operating medium when the blade-angle adjusting mechanism has reached the limit of low blade angle established by said manually operable means.

18. In a system of control for a prime mover propeller power plant, the combination comprising, a member for controlling the operating medium of the prime mover, a propeller blade-angle adjusting mechanism, a speed responsive governor operated by the prime mover, a source of fluid pressure, a valve for distributing iluid flow from said source having a pressure port connected with said source and a pair of control ports, a valve element operated by said governor for controlling the ow of luid kthrough said control ports, a servomotor having a cylinder and piston, said cylinder having chambers which are connected to said control ports, said piston being movable in response to the fluid iow controlled by said governor operated valve element for operating the blade-angle adjusting mechanism to correcta speed error, a second servomotor having a cylinder and a damped piston, passage means connecting opposite sides of the damped piston to enable flow of fluid between the valve element and the rst recited servomotor, said cylinder of the second servomotor having chambers which are connected to said control ports, said damped piston being movable in response to fluid flow controlled by said governor operated valve element for adjusting said operating medium control member while the correction of blade angle is being made yfor effecting stabilization of the governing function, manually operablemeans for setting the operating medium control member for various 'operating medium inputs,V manually operable means for setting the governor for maintaining various speeds, and manually operable means effective in the lower range of blade angle for limiting movement of said rst mentioned piston independently of said governor operated valve lelement whereby the blade-angle adjusting mechanism is unable to decrease the blade angle an amount' demanded by the governor to eliminate under-speed, said damped piston having means connected thereto for electing adjustment of said operating medium control member to increase the "input of operating medium beyond that for which said member is set by the manual control when the blade-angle adjusting mechanism has reached the limit of low blade angle established by said last recited manually operable means.

19. In a system of control for a prime-moverpropeller power-plant, the combination comprising, a propeller blade-angle changing mechanism, a fluid servomotor for controlling the operation of said vmechanism and having a cylinder and piston therein, the displacement of which determines the blade angle, a fiuid pressurepump, a speed responsive valve in circuit connection between said pump and said servomotor` for controlling fluid flow from the pump to either side ofthe piston when there is a speed error, a second Vfluid lservomotor in circuit connection betweensaid first servomotor and said speed responsive valve and having a damped piston, passe ge means connecting opposite sides of the damped piston to A enable flow of fluid between the .valve element and the first recited servomotor, said damped piston vbeing 'movable in response to the f lowofpressure fluid occurring when said rstmentioned piston is moved, and a member operatively vconr'iected with said damped piston and movable thereby for-controlling 'the operating medium input of the prime mover.

20. ln a system o f control for a prime-moverp'ropeller ypoirier-plant, the combination Ycomprising, apropeller blade-angle changing mechanism, a fluid 'servomotor for controlling the operation of said mechanism and having a cylinder and piston therein, the displacement of which determines the blade angle, a fluid pressure pump, a speed responsive valve in circuit connection between 'said pump and said servomotor providing in event ofspeed error, for the distribution of pres- -sure fluid to the *cylinder on either side of the 'piston and for draining of either end of thecylin- 'der as the piston moves toward it, a second cylin- 'der -connected in series with rthe valve and one end'of the first mentioned cylinder, asecvond pis'- ton in the second cylinder, an orifice parallelling lsaid second piston, springs normally 'centering A"said'secor'id piston and opposing movement of the second piston in either direction, said'second-pis- 'ton being movable at a rate proportional to the vfluid flow Vthrough said orifice, vand a member operatively connected with said secondpiston and 'movable thereby for vcontrolling the operatingvmedium input of the prime mover.

21. Tn a system of control for a `prime-mover- 'propeller power-plant, the combination comprising, "a 'propeller 'blade-angle changing mechamism, a fluid servomotor for controlling the opration of 'said mechanism and rhaving a cyliner andpiston therein, the displacement of which "determines "the vblade angle, a fluid pressure pump, `a speed responsive valvein circuit connection between said pump and said -servomotor 4for controlling fluidflow fromthepump to either lsidefof the piston when there isa speed error, fase'cond iluid servomotor in circuit connection lbetween said first servomotor and said speed responsive valve and having a damped'piston, pas- `Sfg'e Incansrjconnecting opposite sides of the` 'dampedfpiston Vto enable flow of fluid betweenv 'the 'valve element'and the rst recited servo- 'moton said damped piston being movable Vin re- 'sponse to the flow 'of pressure fluid occurring 'when said rst mentioned piston is moved, a y'iner'nber operativelyiconnected with said damped piston'and moval'ile thereby for controlling the :operating medium input of the prime mover, 'manually operable means eiective in the'lower 'rangeof blade'anglerforlimitingthe movement I lof said 'first vmentioned piston independently of 28 said speed responsive valve whereby the bladeangle changing mechanism is unable to defcrease the blade angle an amount demanded `by the speed responsive valve to eliminate underspeed, a pressure-relief-valve-controlled b'yp'elss around said first mentioned piston whereby. when movement of the first mentioned piston is arrested by said manually operable means, pres sure fluid will flow from the pump to said second servomotor, said damped piston functioning/in response to the pressure fluid flow last mentioned inconsequence of the unsatisfied demand of the speed responsive valve for blade anglereduction to effect a movement of said member to increase the input of the operating-medium of the prime mover. Y

r 22. In a system of control for a prime-moverpropeller power-plant, the combination comprising, a propeller blade-angle changing mecha.- nism, a fluid servomotor for controllingthe operation of said mechanism and having a cylinder and piston therein, the displacement of which determines the blade angle, a fluid pressure pump, a speed responsive valve in 'circuit connection between said pump and said servomotor providing in event of speed error, for the distribution of pressure fluid to the cylinder on Yeither side of the piston Aand for draining of either end of the cylinder as the lpiston moves toward it, a second cylinder connected in vseries with the valve and one end ofthe first mentioned cylinder, a second piston in the second cylinder 'having an orifice through it, Aspring normally centeringsaid second piston and opposing movement of said second piston in either direction, said second piston being vmovable yat a rate proportional to the fluid flow through said orifice, a memberl operatively connected with said second piston and movable thereby for controlling the operating-medium input 'of `the prime mover, manually operable `means "effective in `the lower range of blade angle-for limiting the 'movement of said vfirst mentioned piston independentlyo'f said speed responsive valve whereby the blade ang-le lchanging vmechanism is unable to decrease the blade angle an amount demanded by the .speed responsive valve to eliminate under'- speed, a pressure-relief-vaIve-controlled 'by-pass 'around said first 'mentioned 'piston whereby, when movement of the first mentioned piston-is arrestedby said manually operable means.pres sure 'fluid will flow from the pump to-said se'- Vond servomotor, said second piston functioning .in `response to the pressure fluid `flow last mentioned in consequence of the unsatisfied demand ofthe speed responsive valve Afor blade angle re- 'duction to effect a movement of 'said member to increase the input of the 'operating-medium of the prime mover.

23. In a control system `for an aircraftpovverplant including a prinie mover and a vpropeller driven thereby having 'variable-pitchibiadeaeaid system comprising a governor driven 'by the -vprimem'overand having speed rsetting meansfn element, 'the lposition of which 'determines the blade-angle, a source of fluid pressreja valve 'for distributing'fluld flow from said-source vhav'- y ing a Apressure port Vconnected Vwith said 'source and a'palrof control-portae valve'plunger'opefated by said-governor for controllingthe flowof rfiuidthrough said ports, a servomotor having a cylinder andupiston,l said cylinder havingcham'- which arewconnected tosaid control ports, said piston beingmovablein response to the fluid flow controlled by said governoroperated valve 

